Field of the Invention:
The invention relates to a production process for a capacitor electrode formed of a platinum metal in an integrated semiconductor circuit.
One example of a semiconductor circuit with a capacitor is a DRAM memory cell. In order to increase the scale of integration thereof, it can be constructed as a so-called stacked capacitor cell, in which the memory capacitor is located outside the associated selection transistor. The choice of the capacitor dielectric, among other factors, has a substantial influence on the space required by such a capacitor.
Conventional capacitors usually use silicon oxide or silicon nitride layers as the storage dielectric, and those layers have a maximum dielectric constant of 8. New paraelectrical materials, such as BST (barium strontium titanate, BaSrTiO.sub.3) and the like have a dielectric constant .di-elect cons.&gt;150 and thus make a smaller capacitor possible.
Such memory elements with a paraelectric material as their capacitor dielectric (DRAM) lose their charge if the supply voltage fails and thus they lose the information stored in them. Moreover, conventional memory elements must be constantly rewritten (refresh time) because of the residual leakage current. The use of a ferroelectric material as a storage dielectric provides different directions of polarization, which makes it possible to construct a nonvolatile memory that does not lose its information if the supply voltage fails and does not have to be refreshed constantly. The residual leakage current from that cell does not affect the signal stored in memory. One example of such a ferroelectric material is PZT (lead zirconium titanate, Pb (Zr, Ti)O.sub.3).
In general, those novel ferroelectrics and paraelectrics are produced at high temperatures in an oxidizing atmosphere. Therefore, a material is needed that is compatible with those conditions, particularly for the first capacitor electrode.
In most cases, an electrode of a noble metal such as platinum, iridium or ruthenium (generally referred to as "platinum metals") is used. However, the structuring of platinum metals, especially with a relatively thick platinum layer, for instance, is so far a largely unsolved problem, since until now no suitable etching process has been developed, and since no volatile platinum compounds appear suitable for RIE processes. Previous etching processes have been based on the application of a resist mask and on etching in argon, oxygen or chlorine plasmas. Due to the high physical component of the process, only slight selectivity with regard to mask materials and the underlying material can be attained.